This invention relates to a continuous process for the preparation of triacetin from glycerol, acetic acid and acetic acid anhydride.
A discontinuous process for the preparation of triacetin in which glycerol and acetic acid anhydride in a molar ratio of 1:3 are reacted at 130.degree. C. to 135.degree. C., is known from German Patent Specification DE-PS No. 347,897. In this reaction, for each mol of reacted glycerol, 3 mols of acetic acid are produced for which there is generally hardly any way of utilization, making this method unsuitable for the large-scale production of triacetin.
Also known are discontinuous methods for the preparation of triacetin from glycerol and acetic acid, as can be learned from the journal, Seifen-Ole-Fette-Wachse, 1962, pp. 597-602. Since the reaction equilibrium is on the side of the starting materials in this reaction, the water produced during the esterification reaction must be removed continuously from the reaction mixture to keep the required acetic acid to a reasonable amount. These methods require long reaction times and therefore have a high energy consumption and a poor utilization of the reactor capacity.
As can be seen from Seifen-Ole-Fette-Wachse, 1962, p. 598, the esterification reaction can be accelerated, especially in the low temperature range from 100.degree. to 160.degree. C., by acid catalysts. The catalyst must have a lower vapor pressure than glycerol to prevent its accumulation in the vapor phase.
In addition, German Published Application DE-OS 19 05 880 describes the production of triacetin from the reaction of allyl acetate with acetic acid and acetic acid anhydride in the presence of a catalyst. Now it was found that the disadvantages of the known methods can be largely eliminated by using the continuous process for the preparation of triacetin described below.